<!DOCTYPE html>
<script src='../../resources/testharness.js'></script>
<script src='../../resources/testharnessreport.js'></script>
<script src='../../resources/gesture-util.js'></script>
<!-- This div is 200 pixels high. The content results in scrool bars on
  both edges, resulting in an effective content area of 185 x 185 on
  linux. The paging context overlap is 24 pixels. So one page of scroll
  moves the content by 185 - 24 -= 161 pixels. -->
<div id="overflow" style="border:2px solid black;overflow:auto;height:200px;width:200px;">
    <div style="height:300px;width:600px">
      <div style="background-color:red;height:300px;width:300px;position:relative;left:0px;top:0px"></div>
      <div style="background-color:green;height:300px;width:300px;position:relative;left:300px;top:-300px"></div>
    </div>
    <div style="height:300px;width:600px">
      <div style="background-color:blue;height:300px;width:300px;position:relative;left:0px;top:0px"></div>
      <div style="background-color:yellow;height:300px;width:300px;position:relative;left:300px;top:-300px"></div>
    </div>
</div>

<script>
    var givenScrollTop = 2; // When paging, this is ignored. Every event is one page.
    var expectedScrollTop = 161;
    var last_event = null;
    var source = GestureSourceType.MOUSE_INPUT;
    const numTicksY = givenScrollTop / pixelsPerTick();
    const expectedWheelDeltaY = numTicksY * LEGACY_MOUSE_WHEEL_TICK_MULTIPLIER;

    function mousewheelHandler(e)
    {
        last_event = e;
    }

    promise_test(async () => {
      const overflowElement = document.getElementById("overflow");
      overflowElement.addEventListener("mousewheel", mousewheelHandler, false);

      await smoothScroll(givenScrollTop, 100, 110, source, 'down', SPEED_INSTANT, false /* precise_scrolling_deltas */, true /* scroll_by_page */);
      await waitFor( () => {
          return overflowElement.scrollTop == window.expectedScrollTop;
      });
      assert_equals(last_event.wheelDeltaY, -Math.floor(expectedWheelDeltaY));
      assert_equals(last_event.wheelDeltaX, 0);
      assert_equals(last_event.wheelDelta, -Math.floor(expectedWheelDeltaY));
    }, "Page-based wheel scrolls provide correct delta in event handler, scrolling on overflow div.");
</script>
